Translating circuit



Sept. 3, 19350, H, T, FRHS 2,013,140

TRANSLATING CIRCUIT Filed Sept. 16, 1952 L 2 ""Yf UNBALANCEDQ BALANCEDCIRCUIT BALANCED CIRCUIT CH I }UNBALANCED CIRCUIT //v VENTOR h. 7? FRI/5AT TORNEV Patented Sept. 3, 1935 PATENT OFFICE TRAN SLATING CIRCUITHarald T. Friis, Rumson, N. J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationSeptemberql6, 1932, Serial No. 633,423

11 Claims.

This invention relates to electrical wave transmission systems and moreparticularly to coupling devices for high frequency signaling systems.

In the design of high frequency signaling systems there is frequentlymet the problem of coupling a balanced circuit to an unbalanced one. Thedifficulty usually involved is prevent the unbalanced circuit, one sideof which may be .at ground potential, from disturbing the electricalbalance with respect to ground of the other circuit. The maintenance ofthe balanced condition at high frequencies such as employed for shortwave radio communication is complicated by the fact that theintroduction of the slightest difference in the capacitance of the sidesof the balanced circuit to ground may materially affect the efficientoperation of the system. So critical are such circuits in this respectthat special attention must be given to the small capacitances existingbetween the windings of transformers and other circuit elements.

An object of the present invention is to provide means for coupling anunbalanced circuit to a balanced circuit without disturbing theelectrical balance of the latter.

Other objects and features of the invention will appear in the followingdetailed description of a specific embodiment of the invention. Theaccompanying drawing shows in Fig. l a coupling device heretoforeproposed; in Fig. 2 a coupling device in accordance with the presentinvention; and in Fig. 3 an application of the coupling device of Fig.2.

Coupling devices of the type shown in Fig. 1, it has been noted, havebeen suggested heretofore. The balanced circuit l is connected to theterminals of a continuous winding L2, L3 which at its midpoint isgrounded. The unbalanced circuit 2 is connected to theparallel-connected windings L1, L4, which are disposed in inductiverelation with the balanced winding and on respectively opposite sidesthereof with their grounded terminals adjacent the line terminals of thelatter winding. With this method of connection, it will be observed thatthe respective sides of the balanced circuit are capacitively connectedto ground through the inherent interwinding capacitances. Thecapacitance C1-2 existing between windings L1 and L2 is effectivelybetween the upper side of the balanced line I and ground, and thecapacitance C34 existing between windings L3 and L4 is, in effect,similarly connected between the other side of the balanced line, I andground. The balance of circuit l is therefore made dependent on an exactequality between these two inherent capacitances.

Referring now to Fig. 2 there is shown a specific embodiment of thepresent invention comprising a balanced transformer, the windings ofwhich are so disposed relatively to each other and so connected as tominimize the possible unbalancing effect of inter-winding capacitances.The balanced circuit I is in this case connected to the adjacentterminals of the windings L2 and L3, the outer terminals of thesewindings being connected together, preferably by virtue of theirrespective direct connections to container 3. Windings L2 and L3 are soarranged as to be inductively in series-aiding relation. Windings L1 andL4 .are arranged on respectively opposite sides of the central windings.Their adjacent terminals are connected together and to the grounded sideof the unbalanced circuit l, preferably by respective direct connectionsto container 3. Their outermost terminals are similarly joined to thehigh potential side of the unbalanced circuit. The winding directions ofL1 and L4 are opposite to each other so that the voltages induced inthese windings are in phase agreement with respect to the unbalancedcircuit. The container 3, which may be of copper or other suitablematerial is used to shield the transformer against externalinterference.

The physical dimensions of the windings and the separation betweenwindings may, of course, be varied within wide limits. In one air-coredtransformer which was found to operate satis factorily at a wave lengthof I approximately twenty meters, windings L2 and L3 were solenoidal isform and comprised two turns each of one-eighth inch copper tubing woundon a three inch form. Windings L1 and L4 comprised four turns of thesame diameter separated approximately an inch from the central windings.The dimensions of shield 3 may be determined by the maximum allowablevalues of the capacitances C1O and C4 o existing between the shield andthe outer turns of windings L1 and L4, respectively. Provision may bemade also for moving the central windings axially so that an exactelectrical balance can be more readily obtained.

Direct capacitive conn tion to ground from the terminals of the balancedcircuit l, as Fig. 2 shows, is substantially eliminated. The possibilityof capacitive unbalance of that circuit is therefore minimized. Of theinter-Winding capacitances that are present, none tend toward unbalance.The capacitance C24 between L2 and L3 shunts the balanced circuit butdoes not affect the electrical symmetry with respect to ground.Capacitances C14 and C34 are terminated at points of ground potential,i. e., the adjacent terminals of windings L1 and L4, respectively. Theyhave no effect on the balanced circuit, however, since their points ofconnection with the latter circuit are the outer turns of windings L2and L3, which, being at the mid-potential of the balanced circuit, arelikewise at ground potential.

The shunt capacitance C2 3 referred to is disadvantageous in somesystems. Its magnitude may be reduced by increasing the separation ofwindings L2 and L3, or by arranging the windings in accordance with theinvention of A. G. Jensen, disclosed in his application for LettersBatent b'earing "Serial No. 632,097 and filed September: 8, 1932.

In other systems, as in that shown in Fig. 3, this capacitance maycooperate with additional shunt capacitive elements to tune the system.In Fig. 3 is shown an application of the transformer of Fig. 2 to adirectional radio receiving system employing a balanced antenna systemA,which may be, for example, of the horizontal double V or rhomboid type.The directional characteristic of the antenna, which depends to alargedegree on the balance of the coupling circuit, is preserved by the useof a transformer T in accordance with the present invention. A condenserC1 connected across the antenna A and the balanced side of transformer Tis used for tuning'purposes. The unbalanced side of the transformer T isconnected through a tuning condenserCz to a transmission line CLcomprising' coaxial conductors '4 and 5, which leads to the remotelylocated radio receiver R.

"Although the present invention has been described with reference to aspecific embodiment of it, it is not thus limited in nature but iscapable of various other embodiments within the spiritand scope of theappended claims.

What is claimed is:

1. In a high frequency transmission system, a balanced circuit and anunbalanced circuit and an air-cored transformer coupling said circuits,said transformer comprising a first pair of windings axially spaced andconnected to said unbalanced circuit in parallel-aiding relation, asecond pair of windings arranged between and in symmetrical relation tosaid first pair of windings; the ad'jaceiit terminals of said secondpair of win'dingsbeing connected to said balanced circuit the otherterminals of said second pair of windings being connected together.

"'2. Ina high frequency transmission system, a balanced circuit, anunbalanced circuit, and a transformer coupling said circuits, saidtransformer comprising a first pair of windings axially spaced andconnected in parallel to said unbalanced circuit, adjacent terminals ofsaid windin gs being connected together and to ground, a second pair ofwindings positioned symmetrically between and in balanced inductiverelation to said first pair of windings, said second pair of wind ingsbeing arranged in series-aiding relation with adjacent terminals thereofconnected to said balan'c'ed circuit.

3. A high frequency air-cored transformer comprising four solenoidalwindings disposed at spaced intervals along a common axis, a pair ofterminals connected to the adjacent ends of the two central windings, aconnection between the other ends of the central windings, meansconnecting the inner ends of the outer of said four windings, meansconnecting the outer ends of said outer windings, and a pair ofterminals con nected to said connecting means.

4. In a high frequency transmission system, a balanced circuit and anunbalanced circuit, and an air-cored transformer coupling said circuit,said transformer comprising a pair of windings connected to saidbalanced circuit, a pair of windings connected. to said unbalancedcircuit, said pairs of windings being in inductive relation andsymmetrically positioned with respect to each other, the ends of saidfirst-mentioned windings adjacent said second-mentioned windings beingat substantially the midpotential of said balanced line.

5. In a high frequency transmission system, a balanced circuit andanother circuit and an aircored transformer coupling said circuits, saidtransformer comprising two pairs of inductively related windings,connections from said balanced circuit to corresponding ends of asymmetrically positioned pair. of said windings, said symmetricallypositioned pair of windings presenting to tlieothers of said windingsonly their low potential ends, and said other circuit being connected tosaid other pair of windings.

6. In a high frequency transmission system, a balanced circuit andanother circuit, and an aircored transformer coupling said circuits,said transformer comprising a multiplicity of windings, two of saidwindings being connected in series with each other and with saidbalanced cir-.- cuit, said two windings being so positioned that thehigh potential ends of said two windings are substantially free frominter-winding capacitances to ground, and connections from a pluralityof the other of said windings to said unbalanced circuit.

'7. In an electrical signaling system, a balanced circuit and anothercircuit, and a transformer coupling said circuits, said transformercomprising a plurality of windings connected to said other circuit andaplurality of windings inductively balanced and symmetrically positionedwith respect to said first plurality of windings and'connected to saidbalanced circuit, the terminals of said second plurality of windingsthat are connected to said balanced circuit being not adjacent windingscomprising said first plurality of windings.

8. A balanced circuit, another circuit, a high frequency transformercomprising four nonoverlapping windings symmetrically disposed along acommon axis, means for connecting a pair of said windings in parallel tosaid other circuit, means for connecting the other pair of saidWindingsin series to said balanced circuit, only the low potential endsof said other pair of wind ings being adjacent said first pair.

9. A combination in accordance with claim 8 in which the low potentialends of said first pair of windings are adjacent the low potential endsof said other pair of windings.

10. In a system for coupling a single ended circuit with a double endedcircuit, comprising a transformer having a pair of primary windings anda pair of secondary windings, one pair of said windings being woundinopposite directions and connected in parallel in said single endedcircuit and the other pair of windings being wound in the same directionand connected in balanced relation in said double ended circuit, and thepoints of zero alternating potential on both pairs of windings beingplaced in close proximity to each other;

11. In a system for coupling a single ended circuit with a double endedcircuit, comprising a transformer having a pair of primary windings anda pair of secondary windings, one pair of said windings being wound inopposite directions and connected in parallel in said single endedcircult and the other pair of windings being wound in the same directionand connected in balanced relation in said double ended circuit, saidpairs of windings being so spaced relative to each other HARALD T.FRIIS.

